Isomeric cresols

Cresols isomeric mixture Cumene Diethylbenzene Divinylbenzene... 

In some cases we may benefit from using an external agent to carry out the desired separation through crystallization. Thus, in the case of isomeric and non-isomeric mixtures of close-boiling acidic or basic materials we may use a suitable base or acid to carry out dissociative extractive crystallization, akin to dissociative extraction referred to in Section 4.2.1. For instance, for a mixture of p- and m-cresol or p-cresol and 2,6-xylenol we may use a base like anhydrous piperazine to obtain a precipitate of relatively pure p-cresol salt of piperazine, which can then be filtered and subjected to recovery of piperazine for recycle. Similarly, we may add a substance which forms an adduct with the desired substance. 

As to the main limitation of MS vs. FTIR detection, namely the inability to distinguish closely related isomers, this rarely plays a role in additive analysis. Notable examples of isomeric additives are the bifunctional stabilisers C22H30O2S as 4,4 -thio-bis-(6-t-butyl-m-cresol), 2,2 -thio-bis-(4-methyl-6-f-butylphenol) and 4,4 -thio-bis-(2-methyl-6-f-butylphenol) (Section 6.3.6), the bisphenolic antioxidants C23H32O2 (Plastanox 2246 and Ethanox 720) and the phenolic antioxidants C15H24O (nonylphenol and di-f-butyl-p-cresol). 

It has been shown e that two mechanisms, elimination-addition (benzyne) and SN2 displacement, are operative in the liquid-phase hydrolysis of halogenatcd aromatic compounds. The formation of isomeric phenols as a result of the availability of the benzyne route makes the reaction of limited synthetic value. The incorporation of the copper-cuprous oxide system suppresses reaction via the benzyne route, so that the present method has general utility for the preparation of isomer-free phenols. For example, >-cresol is the only cresol formed from -bromotoluene under the conditions of this preparation. 

The transport and partitioning of an organic compound in the environment is a function of the physical and chemical properties of that compound and the site-specific characteristics of the environment (e.g., percentage soil organic matter). Based on the environmental correlations with physical properties (Lyman et al. 1982), the physical and chemical properties of the three isomeric cresols are sufficiently similar to indicate that similar transport and partitioning processes will be... 

In the atmosphere, the vapor pressure of the isomeric cresols, 0.11+0.30 mmHg at 25.5 °C (Chao et al. 1983 Daubert and Danner 1985), suggests that these compounds will exist predominantly in the vapor phase (Eisenreich et al. 1981). This is consistent with experimental studies that found all three isomers in the gas phase of urban air samples, but they were not present in the particulate samples collected at the same time (Cautreels and Vancauwenbergh 1978). The relatively high water solubility of the cresol isomers, 21,520- 25,950 ppm (Yalkowsky et al. 1987), indicates that wet deposition may remove them from the atmosphere. This is confirmed by the detection of cresols in rainwater (Section 5.4.2). The short atmospheric residence time expected for the cresols (Section 5.3.2.1) suggests that cresols will not be transported long distances from their initial point of release. 

In water, the isomeric cresols may eventually volatilize to the atmosphere, but volatilization is expected to be a slow process. Based on their Flenry s law constants, which range from 1.2x10 to 8.65x10 atm-m /molecule (Gaffney et al. 1987 Hine and Mookerjee 1975), the volatilization half-life from a model river 1 m deep, flowing at 1 m/sec, witha wind velocity of 3 m/sec can be estimated to range from approximately 30 to 41 days (Lyman et al. 1982). 

Experimental bioconcentration factors (BCFs) of 14.1 for o-cresol (Sabljic 1987) and 19.9 for m-cresol (Freitag et al. 1982) indicate that the isomers of cresol will not bioconcentrate in fish and aquatic organisms to any significant extent. Also, cresols are not likely to bioconcentrate in humans. Similar to their behavior in soil, the isomeric cresols are not expected to adsorb to sediment and suspended organic matter, although the potential for this process exists. 

Methods for determining cresols in environmental media are summarized in Table 6-2. Procedures for the determination of and o- and p-cresol in water, soil, and sediment samples at hazardous waste sites are outlined by EPA (1988a). The required quantitation limits for each of the isomeric cresols are 10 ppb for water samples and 330 ppb for soil and sediment samples in this monitoring program. 

Human exposure to cresol is likely to occur by inhalation or ingestion of contaminated water. Standardized methods for the determination of the isomeric cresols exist for both of these matrices. These methods are both reproducible and sensitive. In addition, acceptable methods for the determination of cresol in other environmental media have appeared in the literature. 

Although the isomeric cresols degrade readily in the environment, their degradation products (Bayly and Wigmore 1973 Masunaga et al. 1983, 1986) are not unique to these compounds (see Section 5.3.2). As a result, the determination of these intermediates cannot be accurately extrapolated back to levels of cresol contamination in the environment. 

Fraction 8 (Figure 5 5) is mostly alkylated phenols and indanols with a trace amount of smaller alkanes. The base line shift is due to the co-elution of several large phenolic species in many isomeric forms. Fraction 9 (Figure 5-6) does not contain any alkanes. The ratio of the o-cresols to m, p-cresols increases from fraction 8 to 9. Both m-cresol and p-cresol are structurally longer than o-cresol. Some long aromatic species such as biphenyls also appear in this fraction. Compared to fraction 8, the phenols in fraction 9 are of shorter size... 

Problem 11.30 Account for the observation that NaOH reacts at 300 "C with p-bromotoluene to give m- and p-cresols, while m-bromotoluene yields the three isomeric cresols. A... 

The benzyne intermediate from p-bromotoluene has a triple bond between and C" both C s are independently attacked by OH, giving a mixture of m- and p-cresols (HOCtH CH,). Two isomeric benzynes are formed from m-bromotoluene, one with a C -to-C triple bond and the other with a C -to-C" triple bond. Hence, this mixture of benzynes reacts with OH at all three C s, giving the mixture of three isomeric cresols. 

A mixture of three isomeric cresols is used in a commercially available cresol-formaldehyde Novolak resin. This mixed Novolak resin, Varcum resin (12), provides adequate properties as a host resin for near-UV- and mid-UV-photoresist applications. Gipstein and his co-workers prepared pure cresol-formaldehyde Novolak resin from each isomeric cresol and compared their spectroscopic and resist characteristics (13). Their data on the UV-absorption spectra of each cresol-formaldehyde Novolak resin together with the commercially available Varcum resin are as follows the absorbances of 0.2 jim thick Novolak films at 250 nm are 0.165(Varcum), 0.096(o-cresol), 0.092(m-cresol), and 0.055(p-cresol). The so-called "window" in the UV absorption at around 250 nm is a maximum with the p-cresol-formaldehyde Novolak resin, while the other isomeric cresol and formaldehyde Novolak resins yielded similar UV absorptions at this wavelength. The smallest UV absorption at 254 nm is an advantage for the p-cresol-formaldehyde Novolak when the resin is used for a deep UV photoresist with a suitable photoactive compound (14). 

Sulfonation of Benzene and Alkylbenzenes. Since the main utilization of ben-zenesulfonic acid was its transformation to phenol, the importance of the sulfonation of benzene has diminished. The process, however, is still occasionally utilized since it is a simple and economical procedure even on a small scale. Excess sulfuric acid or oleum is used at 110-150°C to produce benzenesulfonic acid.97,102 Sulfonation of toluene under similar conditions yields a mixture of isomeric toluenesul-fonic acids rich in the para isomer. This mixture is transformed directly to cresols by alkali fusion. 

For toluene, Atkinson et al. [142] have obtained an o-cresol yield of 13 7%, independent of total pressure from 62 to 740 Torr of air. When combined with the o-cresol/total cresol formation ratio of approx. 0.8 [149,150], this leads to a total isomeric cresol yield of approx. 16 8%. 

Phenols in tobacco smoke (hydroxyquinone, resorcinol, catechol, phenol, isomeric cresols)... 

Uses Cresol is a mixture of three isomeric forms, namely, ortho-, meta-, and paracresol. Cresol is a colorless, yellowish, brownish yellow, or pinkish liquid with a phenolic odor. It is used as an ore flotation agent and as an intermediate in the manufacture of chemicals, dyes, plastics, and antioxidants. It also is used in the manufacture of dyes, paint removers, plastics, stains, resins, chemical disinfectants, flotations, foundries, wool scours, and insulation enamels. 

Isomerization of arene oxides to phenols proceeds by complex and often multiple pathways660 668 that show a marked dependence on pH. Arene oxides as key intermediates provide the basis for explaining the ortho/meta/para isomer ratios observed in enzymatic hydroxylations.655a,b For example, the absence of m-cresol in the metabolites of toluene can be attributed to the fact that none of the three possible isomers of toluene oxide rearranges to this product. 

Of the three isomeric cresols ortho-, meta-, and para-, only m- cresol can be used as the starting material for introducing three nitro groups, viz. in the 2,4,6-positions. Ortho and p- cresols are able to form stable nitro group systems only when no more than two nitro groups are introduced. Under the conditions of the nitration of m- cresol to its trinitro derivative the o- and p- isomers are oxidized to oxalic acid. 

Ketones arise from phenols by isomerization of unsaturated alcohols (37). Palladium is the most suited for this type of reaction because of its high isomerization activity coupled with a very low rate of reduction of the resulting ketones (6). Excellent yields of ketones often may be obtained rhodium will give at times quite substantial yields of cyclohexanones (50-65% methylcyclohexanones from cresols) (38), but in other reductions such as resorcinol, little ketone accumulates over either rhodium or platinum under conditions where it is a major product over palladium (29). 

Catalytic hydrogenation in the vapor phase of isomeric cresols over nickel catalysts at a high temperature leads to alcohols rich in the equatorial isomer. 

TABLE 11.9 The Selectivities for the Formation of Cyclohexanone Intermediates in the Hydrogenation of Isomeric Cresols and the Relative Reactivities of the Ketone to Cresol over Ru, Rh, and Pd-C Catalystfti>... 

Alkylphenols may be produced via the alkylation of phenol with methanol. This reaction produces predominantly anisole and o-cresol with methylanisole and xylenol also being obtained. Strong Bronsted acids are not required to effect these transformations, as both amorphous aluminas and silica/aluminas are active catalysts. Often o-cresol can be produced in 100% isomeric selectivity, particularly when the reaction is run over amorphous alumina based catalysts. When zeolites are used isomer selectivities are changed. 

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